[BUGFIX] megapony-object-valign-middle: Total width of child is not always 100%

* Adds additional class "full-width" for special valign objects (see example 1 in the changed demo)
* Adds demo examples for 2 different cases (WITH optional "full-width" class & WITHOUT the class)
* Disables no-side-by-side behaviour for full-width valign-middle objects (behaviour's just like tables behaves), enabled only for fixed width cells

Fixes #10